1. Field of the Invention
The present invention relates to a liquid-crystal display apparatus and a three-panel liquid-crystal display projector.
2. Description of the Related Art
Referring to FIG. 10, a three-panel liquid-crystal display projector employs three liquid-crystal display panels 1R, 1G, and 1B as optical shutters. A high-intensity white light from a metal halide lamp or the like is separated through dichroic mirrors (not shown) or the like into red, green and blue light rays. Receiving the red, green and blue light rays, the respective liquid-crystal display panels 1R, 1G, and 1B output a red video image, a green video image and a blue video image. The red, green, and blue video images are synthesized through a dichroic prism 2, and the synthesized image is then projected onto a screen 4 through a lens system 3. An enlarged projected color image is thus obtained.
Such a three-panel liquid-crystal display projector suffers from on-screen chrominance non-uniformity in the display on the screen 4, because of non-uniformity in light transmissivity in the optical systems 2 and 3, and the liquid-crystal display panels 1R, 1G, and 1B.
In the three-panel liquid-crystal display projector, as shown in FIG. 10, the red video image and the blue video image are respectively left-side-right inverted at each of the dichroic prism 2 and the lens system 3, but the green video image is inverted by the lens system 3 only, and the green video image only is projected in a left-side-right inverted orientation.
Now there is a variation in luminance in a horizontal direction in the light source or the optical systems. The green video signal only is inverted left side right, and the red video image and the blue video image are superimposed on the green video image, as shown in FIG. 11. When a gray color display is presented, the right hand side becomes greenish gray, and the left hand side becomes magenta gray, as shown in FIG. 11. A similar phenomenon occurs when the red video image or the blue video image is inverted.
Another cause for the chrominance non-uniformity on the display screen is a variation in light transmissivity, due to a interlayer gap variation present in the liquid-crystal display panel, called Newton's rings, as shown in FIG. 12.
An electrical signal processing system in the conventional three-panel liquid-crystal display projector is unable to remove the chrominance non-uniformity, because brightness adjustment, gain adjustment and a liquid-crystal display panel common voltage remain fixed throughout a horizontal display period and a vertical display period.